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Commit 37e82c2f authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by David S. Miller
Browse files

bpf: allow BPF programs access skb->skb_iif and skb->dev->ifindex fields 



classic BPF already exposes skb->dev->ifindex via SKF_AD_IFINDEX extension.
Allow eBPF program to access it as well. Note that classic aborts execution
of the program if 'skb->dev == NULL' (which is inconvenient for program
writers), whereas eBPF returns zero in such case.
Also expose the 'skb_iif' field, since programs triggered by redirected
packet need to known the original interface index.
Summary:
__skb->ifindex         -> skb->dev->ifindex
__skb->ingress_ifindex -> skb->skb_iif

Signed-off-by: default avatarAlexei Starovoitov <ast@plumgrid.com>
Acked-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent e01ec219

include/uapi/linux/bpf.h

+2 −0
Original line number Diff line number Diff line
@@ -236,6 +236,8 @@ struct __sk_buff { 
	__u32 vlan_tci;

	__u32 vlan_proto;

	__u32 priority;

	__u32 ingress_ifindex;

	__u32 ifindex;

};



#endif /* _UAPI__LINUX_BPF_H__ */

net/core/filter.c

+18 −0
Original line number Diff line number Diff line
@@ -1499,6 +1499,24 @@ static u32 sk_filter_convert_ctx_access(int dst_reg, int src_reg, int ctx_off, 
				      offsetof(struct sk_buff, priority));

		break;



	case offsetof(struct __sk_buff, ingress_ifindex):

		BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, skb_iif) != 4);



		*insn++ = BPF_LDX_MEM(BPF_W, dst_reg, src_reg,

				      offsetof(struct sk_buff, skb_iif));

		break;



	case offsetof(struct __sk_buff, ifindex):

		BUILD_BUG_ON(FIELD_SIZEOF(struct net_device, ifindex) != 4);



		*insn++ = BPF_LDX_MEM(bytes_to_bpf_size(FIELD_SIZEOF(struct sk_buff, dev)),

				      dst_reg, src_reg,

				      offsetof(struct sk_buff, dev));

		*insn++ = BPF_JMP_IMM(BPF_JEQ, dst_reg, 0, 1);

		*insn++ = BPF_LDX_MEM(BPF_W, dst_reg, dst_reg,

				      offsetof(struct net_device, ifindex));

		break;



	case offsetof(struct __sk_buff, mark):

		return convert_skb_access(SKF_AD_MARK, dst_reg, src_reg, insn);